The present invention relates to a method and a system for controlling a build-up rate at which brake pressure increases till completion of pressure build-up for stand-by brake torque applied to an automotive vehicle during stand-by brake torque control under a condition of approaching or following an obstacle preceding the vehicle. The term xe2x80x9cobstaclexe2x80x9d is used herein to mean a stationary or moving object within the path of the vehicle, for example, vehicles, pedestrians, etc. The term xe2x80x9cstand-by brake torquexe2x80x9d is used herein to mean a brake torque, i.e., a negative torque, applied to a vehicle in anticipation of operator braking action or when operator braking action is imminent under a condition of approaching or following an obstacle preceding the vehicle. The term xe2x80x9coperator braking actionxe2x80x9d is used herein to mean vehicle operator or driver action to operate a brake pedal with intention to lower traveling speed of a vehicle.
JP-A 7-144588 discloses a system whereby traveling speed and deceleration of an obstacle preceding a host vehicle are determined using a Doppler sensor and a vehicle speed sensor, which are on the vehicle, and a desired distance from the obstacle is determined. In this system, a vehicle operator is warned and an automatic braking action is initiated if the distance from the obstacle becomes less than the desired distance.
Various control schemes for braking of a vehicle are known in he art. One such example, as disclosed in JP-A 11-175898, is substituting the output of a millimeter wave radar for the output of a laser radar if the latter fails, and setting a different set of thresholds upon comparing to the output of the millimeter wave radar from an initial set of thresholds for comparison to the output of the laser radar. Another example, as disclosed in JP-A 8-80822 or JP-A 10-59150, is initiating partial activation of a vehicle braking system when the time rate of change of throttle angle upon operator releasing the accelerator pedal exceeds a predetermined level.
In the above-mentioned examples, comparing thresholds to the output of the radar or comparing the predetermined value to the time rate of change of throttle angle to initiate braking action. Various other measures to determination of the initiation of braking action are known in the art. One such example is proposed by the assignee of the present invention and described in IP-A 10-24818. According to this proposal, an axial thrust applied to a steering shaft from a steering wheel is monitored for comparison to a threshold in anticipation of axial load applied to the steering wheel by an operator during his/her leg motion to step on a brake pedal. Comparing the monitored axial thrust to the threshold is used to determine the level of emergency of braking. Another example is monitoring the strength of operator grasping a steering wheel to determine the level of emergency as disclosed in JP-A 11-286264. Still another example is proposed by the assignee of the present invention and described in JP-A 11-5528 or JP-A 11-255087. This example is monitoring the strength of operator stepping on a footrest to determine the level of emergency. Other example is proposed by the assignee of the present invention and described in JP-A 5-112158.
The conventional systems are satisfactory to some extent, but a need still remains for developing stand-by brake torque control in a direction to provide enhanced response of a brake system to operator action for braking without impairing operator ride feel.
An object of the present invention is to provide a system and a method for stand-by brake torque control, which provides enhanced response of a brake system to operator depression of a brake pedal without impairing operator ride feel.
According to one aspect of the present invention, there is provided a system for stand-by brake torque control wherein brake pressure increases till completion of pressure build-up for stand-by brake torque applied to an automotive vehicle under a condition of approaching or following an obstacle preceding the vehicle, the system comprising:
an obstacle recognition system detecting a distance to the obstacle preceding the vehicle;
a vehicle speed sensor detecting traveling speed of the vehicle;
an accelerator operable by an operator of the vehicle;
an accelerator sensor detecting operator demand for vehicle acceleration from motion of the accelerator;
an operator reaction responsive sensor detecting reaction by the operator; and
a controller programmed
to perform stand-by brake torque control before operator action for braking,
to select one of predetermined different emergency levels in response to at least one of the detected distance the detected traveling speed, the detected operator demand, and the detected reaction, and
to determine one of various variation rates in response to the selected one emergency level for initiating the stand-by brake torque control by increasing brake pressure at the determined one variation rate till completion of pressure build-up for stand-by brake torque applied to the vehicle.
According to another aspect of the present invention, there is provided a method for stand-by brake torque control wherein brake pressure increases till completion of pressure build-up for stand-by brake torque applied to an automotive vehicle under a condition of approaching or following an obstacle preceding the vehicle, the vehicle having an accelerator and a brake pedal, the method comprising:
initiating stand-by brake torque control upon determination of one of events that include recognition of emergency, operator reaction, and quick release of the accelerator;
determining a variation rate at which brake pressure increases till completion of pressure build-up for stand-by brake torque applied to the vehicle in response to time left before the vehicle operator depresses the brake pedal after determining the one event; and
increasing brake pressure at the determined variation rate till completion of pressure build-up for stand-by brake torque before the vehicle operator depresses the brake pedal.